1. Field of the Invention
Embodiments of the invention relate to a zoom lens system, an imaging optical device, and a digital apparatus. For example, one or more embodiments of the present invention relate to the following: a telephoto zoom lens system as an imaging optical system having a variable magnification function such that an angle of view at a telephoto end is about 5° and a shake-proof function; an imaging optical device that outputs, as an electrical signal, a picture of a subject taken in with the zoom lens system and an imaging element; and a digital apparatus having an image input function, such as a digital camera, that incorporates such an imaging optical device.
2. Description of Related Art
In recent years, in the field of digital single-lens reflex cameras, especially in the field of mirrorless single-lens cameras, there have been increasing demands for reduction in size and weight of cameras including interchangeable lenses. However, in a zoom lens system whose angle of view at the telephoto end is about 5°, the total length of the zoom lens system tends to be increased. Furthermore, due to a long focal length with respect to an imaging surface diagonal length of an imaging element, such a zoom lens system also causes a large amount of image blur on the imaging surface when camera shake occurs, resulting in failed photography. There have been proposed zoom lens systems that correct image blur by moving part of the optical system in a direction perpendicular to an optical axis in, for example, Patent Literatures 1 and 2.    Patent Literature 1: Japanese Patent Application Publication No. 2001-117000    Patent Literature 2: Japanese Patent Application Publication No. 2003-295059
Telephoto zoom lens systems disclosed in Patent Literatures 1 and 2 listed above perform camera-shake correction by moving an entire third lens group. However, application of configurations disclosed in Patent Literatures 1 and 2 to a large imaging element is accompanied by increased size of a shake-proof mechanism and increased weight resulting from a large number of lens elements used in such configurations.